Significance of the River Dirce in Antigone

My students have been reading Antigone, by Sophocles, and recently I asked them to do a close reading of the Parados as one of their blog posts. For the most part, the blog posts were right on track. Students were identifying metaphors and personification. But one question seemed to stump most--if not all--of my students. I believe it was simply because they didn't dig deep enough in their research for the question, choosing instead to stick with the first answer they found. And maybe stump is too harsh a word, they just needed to push a little bit more and they would have had it. Now to the question:

What is the significance of Polynieces and Etocles fighting in the river Dirce?

Most students were able to re-tell the story of Dirce in mythology, but failed to find the information that all Theban kings were sworn into office while standing before Dirce's tomb. Thus, Polynieces and Etocles fighting each other--over the Theban crown, no less--in the river Dirce, becomes symbolic because they are fighting for the right to rule in the river named after the tomb where they swear in Theban kings. 

Antigone is usually pretty straight forward, not a lot of symbols or literary devices. But, in the Parados we have this rich symbolism where we get more by understanding the mythology 

One student got it right though. Check out her blog posts here:
http://susiequeen16.blogspot.com/